Vortex phases and glassy dynamics in the highly anisotropic superconductor HgBa2CuO4+δ

We present an extensive study of vortex dynamics in a high-quality single crystal of HgBa2CuO4+delta, a highly anisotropic superconductor that is a model system for studying the effects of anisotropy. From magnetization M measurements over a wide range of temperatures T and fields H, we construct a detailed vortex phase diagram. We find that the temperature-dependent vortex penetration field H-p(T), second magnetization peak H-smp(T), and irreversibility field H-irr(T) all decay exponentially at low temperatures and exhibit an abrupt change in behavior at high temperatures T/T-c > similar to 0.5. By measuring the rates of thermally activated vortex motion (creep) S(T, H) = vertical bar dInM(T, H)/dInt vertical bar, we reveal glassy behavior involving collective creep of bundles of 2D pancake vortices as well as temperature- and timetuned crossovers from elastic (collective) dynamics to plastic flow. Based on the creep results, we show that the second magnetization peak coincides with the elastic-to-plastic crossover at low T, yet the mechanism changes at higher temperatures.